The present invention relates generally to fish detecting equipment of the type commonly used by fishermen to detect the presence and movement of fish in the vicinity of a fishing boat and, more particularly, to a Doppler fish-finder utilizing a directional sonic transducer.
Most commercially available fish detecting systems operate on the well-known "Doppler" principle, wherein a sonic signal is transmitted in a directional beam into surrounding water by means of a transmitting transducer. Sonic signals from the surrounding water resulting from reflections of the transmitted signal are received by a directional receiving transducer. Typically, the transmitting and receiving transducers are combined within a single directional transducer assembly If a reflected signal is received from a moving object in the surrounding water, the return signal will be shifted in frequency because of the "Doppler" effect. By electronically processing the frequency shift, the fisherman is provided with information concerning the presence and general location of a moving fish and objects within the beam of the transmitted sonic signal.
Prior art directional Doppler detection systems have become very popular with fishing enthusiasts, both amateur and professional. However, the utility of these prior art systems has been limited to some extent by the characteristic narrow beam directional transducer and the method of mounting it to the fishing boat. Typically, the transducer is mounted to the hull of the boat either temporarily, as by a suction cup, or permanently, as by a bracket attached to the boat. In either case, the transmission beam is directed downwardly. Consequently, the area of coverage is small and can only be expanded by moving the boat.
In U.S. Pat. No. 3,123,798, issued to Holloway et al, a portable fish-finder is disclosed including a directional transducer mounted to the end of a suitable handle. The angle between the transducer and the handle is selectively fixed by means of a bolt and wing nut that couple the two parts together. Although the disclosed handle arrangement permits the operator to direct the transducer beam to some extent, the apparatus must be held during use. Furthermore, no indication of the beam orientation is provided the operator.
The ultrasonic Doppler fish detector disclosed in U.S. Pat. No. 4,538,249, issued to Richard, provides for radial detection coverage with a directional transducer by mounting the transducer to a rotatable vertical shaft that is operably clamped to the side of a boat. In one embodiment, the transducer is attached to the lower drive housing of an electric trolling motor. Likewise, U.S. Pat. No. 3,885,338, issued to York, discloses a signalling apparatus for controlling the movement of pelagic fish, wherein a directional acoustic transducer is mounted to the end of a rotatable vertical shaft that is clamped to the side of a boat. A bearing indicator is provided to indicate the direction of the transmitted beam.
Efforts to overcome the disadvantages associated with narrow beam transducers for Doppler detection systems have also included the development of so-called wide beam and omnidirectional transducers. Although expanded somewhat, the coverage area for each of these types of transducers is still limited to some extent. Also, these special types of transducers are not necessarily compatible with existing directional Doppler detection systems and may require circuit modifications and/or enhancements.
The present invention is directed to overcoming the aforementioned problems associated with prior art fish detecting equipment, wherein it is desired to provide an improved mounting apparatus for the directional sonic transducer of a Doppler fish-finder.